Electric hoist.



G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR. 13. 1912.

Patented Nov. 17, 1914.

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3 SHEETS SHEET 2 G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR. 13 1912- sz l z za Zz G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR.13. 1912.

3 T B E H A s T B E H S WITNESSES flaw-44 THE NORRIS PEYERS CO,PHOTO-LITNQ. wasnuvc; rvN. D. c

GUY K. MITCHELL, OF BALTIMORE, MARYLAND.

ELECTRIC I-IOIST.

Specification of Letters Patent.

Patented Nov. 17, 1914.

Application filed March 13, 1912. Serial No. 683,576.

To all wk am it may concern:

Be it known that I, GUY K. MITCHELL, a citizen of the United States,residing at Baltimore, in the State of Maryland, have invented certainnew and useful Improvements in Electric Hoists, of which the followingis a specification.

This invention relates to power driven hoists or elevators and moreparticularly to electrically operated elevators of the type commonlyknown as dumb waiters.

One object of the invention is to provide a silent and eilicient drivefor such machines and to so arrange the gearing that the speed ratiobetween the motor and cable sheave may be varied as desired.

Another object is to provide an improved arrangement of manual controlfor starting, stopping and reversing the machine.

A still further object is to provide means for automatically shuttingoff the power from the motor as the car approaches the limits of itsmovement, such means being designed especially to prevent over-throwingof the control Wheel in machines where the car travels at comparativelyhigh speed.

lVith the above and other objects in view, and to improve generally thedetails ofconstruction of such machines, the invention consists in thearrangement hereafter described and claimed, and shown in theaccompanying drawings, in which,-

Figure 1 is a plan View of my improved dumb waiter machine complete;Fig. 2 is a sectional detail showing a modified constructions; Fig. 3 isa front elevation of the brake, the cam shaft being shown in section;Fig. 1 is a transverse section of the machine substantially on the lineas of Fig. 1; Fig. 5 is an end elevation of the machine as shown in Fig.1; Fig. 6 is a diagram of thecircuit connections employed; and, Fig. 7is a diagram showing the improved arrangement of control ropes.

Referring to the drawings in detail, 1

designates a suitable frame constituting a base or support on which themechanism is carried. An electric motor 2, preferably of the shunt type,is mounted on one end of the frame, with the commutator housing 2 on theoutside. On the inner end of the shaft 3 of the motor is secured afriction disk 4, the face of which is adapted to be engaged by theperiphery of a friction wheel 5, which is secured to a drive shaft 6 bymeans of a key or feather 7. By adjusting the position of the wheel 5along the shaft 6, it may be caused to engage the face of the disk 4-.at points more or less removed from the center thereof, and by thismeans the speed ratio between the motor shaft and drive shaft may bevaried as desired. The shaft 6 is mounted in journals 8 which slide inWays 9, and are urged toward the motor as by means of springs 10. Thefriction wheel is thus caused to firmly contact with the disk 1. Rigidlymounted upon the shaft (3 is the @able sheave 11 over which passes thedriving rope to which the car and counterweight are attached. As shown,the shaft 6 is at right angles to the motor shaft 3, but by usingspecially beveled friction wheels the angle may be aried as desired.

J ournalcd in bearings 13 is a controlling shaft 12. This is preferablyin the form of a cam shaft consisting of a solid cylindrical bar havingsegments 14- cut or milled out as clearly shown in Fig. 1, such segmentsbeing arranged alternately on opposite sides of the bar for the purposehereinafter described. Near one end the shaft has two segments cut fromopposite sides of the ba at the same point as indicated at 15, andadjacent this end also is a similar flattened portion 16 (see Fig. 3) inwhich the cut out portions are arranged at right angles to thoseindicated at 15. adapted to be engaged by a pair of arms 17 projectingfrom a hand brake 1S, hinged at 19 to the frame 1 and adapted to embracethe periphery of the friction disk 1. The arms 17 are normally urgedtogether so as to apply the brake by means of a compres sion spring 20,which encircles a bolt 21 which passes through the arms 17, the springbeing arranged between one arm and a nut on the end of a bolt.

The direction of rotation of the motor and the starting and stoppingthereof is controlled by means of a set of reversing switches 22. Afield switch 23 is also provided for controlling the circuit of theshunt field, as will be hereinafter described.

Each of the switches consists of a pivoted arm carrying at one end acontact surface adapted to engage a fixed contact 2 1. Each of theswitch arms is pivoted at to a bracket, such brackets, as well as thecontacts 24, being mounted upon a slab 28 of slate or other insulatingmaterial. Under each arm on the side of the pivot remote from thecontact 24;, is arranged a compression The flattened portion 16 is,

spring 26, which tends to move the arm so as to bring the contacts intoengagement and close the switch. Each of the switches is provided at itsend opposite the contact with a roll 27 which engages the lower surfaceof the cam. shaft 12, as clearly shown in Fig. 4. As long as the roller2? is in engagement with the cylindrical portion of the shaft, theswitch is held open, but when such roller enters the segment shaped cutout portions 14 or 15 the spring 26 is permitted to move the switch arm.to closed position.

In order to prevent the possible flashing of sparks from the contacts 24and to reduce fire risks, the supporting slab 23 and the switches andcontacts carried thereby are all inclcsed within a fire proof tray orpan 29, as clearly shown in 4. This pan is preferably made of sheetmetal.

30 designates an automatic starting device of any well known type, whichis placed in the armature circuit to limit the rush of current thereinat the moment of starting, or if the load becomes excessive. Thisstarter is also preferably inclosed in a fire proof tray or pan 31,similar to that shown at 29.

On the end of the cam shaft 12 is mounted a control wheel 32 over whichpasses "the manual control rope by means of which the cam shaft isoperated and the movements of the motor and car controlled.

As shown in the drawing, the cam shaft is illustrated in its neutral orstop position. In this position it will be observed that all of therollers 27 engage with cylindrical portions of the cam shaft, andconsequently all of the switches 22 and 23 are opened. Means areprovided for yieldingly maintaining the wheel 32 in this position andfor preventing over-throwing thereof by the hand rope. As shown, suchmeans consists in the provision of a notch 33 in the periphery of thewheel 32, which notch is adapted to be engaged by a roller 34 carried bya lever 35, pivoted at one end 36 to a suitable support 38, and providedat the other end with either a spring (not shown) or a weight 37.

While the apparatus, as shown in Fig. 1, is suitable for some purposes,I prefer to use, where space permits, the arrangement shown in Fig. 2.In this arrangement the bearings 8, Fig. 1, are made fixed, the springs10 being omitted. The motor shaft, however, is extended beyond thecommutator.

housing 2 as indicated at 3, and at such extended end is formed ananti-friction thrust bearing 41 which preferably consists of a pair ofdisks having a raceway and antifriction balls between them. Acompression spring 42 bears upon. the outer of these disks and thedegree of pressure can be regulated by meansof a set screw 43, which iscarried by a casing 40 inclosing the thrust bearing. It will be observedtherefore that the spring 42 constitutes "means for urging the motorshaft and disk 4 toward the friction wheel 5. This construction is morecompact and simpler than the provision of sliding bean the switches inthe position they will assume when the rope wheel 32 is turned 90degrees to ard the righ from the position shown in F l and The cut outportions 14 of the cam shaft pe nit the switches a and c to close, whileof thecut "out portions 15 permits the switcl'i to close simultaneously.Current flows from the conductor j to switch 0, thence from contact cover the connection 9, (indicated in dotted lines, and being made on theback of the slab 28) to contact 6, thence through conductor it, toarmature 2' of the motor,- thence through conductor y' to contact a,switch a, connection. 70, conductor Z, through the auto matic starter30, conductor in, andback to the other side of the line at a. Currentalso simultaneously passes from conductor f through the connection "0,switch 6, Contact 0, conductor p, shunt field winding q to the otherside of the line at at. The motor then runs in such a direction as to(say) raise the car. When it is desired "to stop the car the hand ropeis moved so as to turn the wheel back to the position shown in Fig. 1.When it is desired to lower the car the rope is moved so as to turn thewheel 32 90 degrees to the left, from the position shown in Fig. 1. Thispermits switches Z) and (Z to close, as well as the switch 23, and themotor then runs in the rei e'r's'e direction. It will be seen thereforethat the field switch 23 is closed when the cam shaft is moved in eitherdirection from the stop position, and that two of the switches 22"ar'eclosed for one direction of rotation, and the other two for the otherdirection.

In Fig. 7, 44 designates the usual hand rope which passes over the wheel32 at one end, and over an idler 45 at the other end of the shaft.Ordinarily, as heretofore constructed, it has been common to provideknocker balls on the rope 44 so arranged as to be engaged the car as itapproaches the limits of its travel so as to automatically bring thewheel 32 back to neutral position and thus shut off the power. caroperates at high speed, however, great difliculty has been found inractice on account of the over thro'wi'n'g of such wheel past the stopposition. It is with a view to overcoming this difiiculty that I haveprovided the arrangement shown in Fig. 7.

Where the 5 the other end around a wheel 49. Secured to the wheel 49 isa small sprocket wheel 48 which is geared by means of a chain 47 orother suitable gearing to a larger sprocket wheel 46, rigidly connectedwith the shaft 12 or wheel 32. Knocker balls 52 and 53 are secured tothe rope and are adapted to be engaged by a projection 54 carried by thecar 55.

By virtue of the reduced speed gearing between the wheel 49 and thewheel 32 it will be seen that the rope 50 will have a much greatertravel than the rope 44. Suppose, for example, that the ratio betweenthe wheels 48 and 46 is one to three. This would mean that afterengaging the knocker ball, the car could move say six feet withoutmoving the control rope 44 more than two feet. In other words, by theemployment of such reduction gearing, the car is given a much greaterdistance in which to come to rest after striking the knocker ball thanwould be possible where the knocker balls are mounted directly upon themanual control rope 44. Therefore, with my improved arrangement it is nomore difficult to automatically stop a high speed car than it is toautomatically stop a low speed car with the old arrangement. I regardthis as one of the important features of my invention.

From the foregoing it will be seen that I have provided an improved dumbwaiter machine having an adjustable silent drive and having improvedcontrolling means whereby current is entirely cut oil from the motorwhen the machine is idle, and it is thought that the many advantages ofmy invention will be readily appreciated by those familiarwith therequirements of such apparatus.

What I claim is 1. In an electric hoist, a motor, a drive shaft, gearingtherebetween, a cable sheave on said drive shaft, a car, controllingswitches for said motor, a rotary cam shaft for operating said switches,a rope wheel secured to sald cam shaft, and means whereby the rope wheelis turned by said car as the latter approaches its limiting positions,said rope wheel having a notch in its periphery, and a lever having aprojection adapted to engage said notch, whereby overthrowing of saidrope wheel pastthe stop position is prevented.

2. In an electric hoist, a motor, a driving disk secured to the end ofthe motor shaft, a cable sheave adapted to be driven by such disk, abrake engaging the periphery of said disk, and comprlsing a pair ofpivotallyconnected arms controlling switches for said motor, and arotary cam shaft for operating said switches, said cam shaft comprisinga straight cylindrical bar having a segment cut out adjacent eachswitch, said bar being also cut out adjacent said brake, and extendingbetween the arms thereof to control the same.

3. In an electric hoist, the combination with the motor and cable sheafand car, of a plurality of switch elements controlling said motors, abrake acting directly on the motor armature, a rotary cam shaft tosimultaneously actuate said switches and brake, a rope wheel secured tosaid cam shaft, said wheel having a notch in its pe-' riphery, a leverpivoted at one end and weighted at the other, and having intermediateits ends a projection adapted to engage said notch and thus arrest saidrope wheel and cam shaft in stop position, and

means whereby the rope wheel is turned by said car as the latterapproaches its limitin positions.

In testimony whereof I afiix my signature, in presence of two witnesses.

GUY K. MITCHELL.

\Vitnesses:

KATHARINE H. Roonns, NonL L. BURNS.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

Washington, D. C.

